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If you have 50 different plug types, appliances wouldn't be available and would be very expensive. But once an electric outlet becomes standardized, many companies can design appliances, and competition ensues, creating variety and better prices for consumers.
-- Bill Gates Teste

You are given a non-empty list of integers. For this task, you should return an Iterable consisting of only the non-unique elements from the initial list. To do so you will need to remove all unique elements (elements which are contained in a given list only once). When solving this task, do not change the order of the list. Example: in [1, 2, 3, 1, 3] elements 1, 3 are non-unique and result will be [1, 3, 1, 3].


Input: List of integers.

Output: Iterable of integers.


assert list(checkio([1, 2, 3, 1, 3])) == [1, 3, 1, 3]
assert list(checkio([1, 2, 3, 4, 5])) == []
assert list(checkio([5, 5, 5, 5, 5])) == [5, 5, 5, 5, 5]
assert list(checkio([10, 9, 10, 10, 9, 8])) == [10, 9, 10, 10, 9]

How it is used: This mission will help you to understand how to manipulate lists, something that is the basis for solving more complex tasks. The concept can be easily generalized for real world tasks. For example: if you need to clarify statistics by removing low frequency elements (noise).

You can find out more about Python arrays in one of our articles featuring lists, tuples, array.array and numpy.array.

0 < len(data) < 1000

Invalid hot key. Each hot key should be unique and valid
Hot keys:
CheckiO Extensions

CheckiO Extensions allow you to use local files to solve missions. More info in a blog post.

In order to install CheckiO client you'll need installed Python (version at least 3.8)

Install CheckiO Client first:

pip3 install checkio_client

Configure your tool

checkio --domain=py config --key=

Sync solutions into your local folder

checkio sync

(in beta testing) Launch local server so your browser can use it and sync solution between local file end extension on the fly. (doesn't work for safari)

checkio serv -d

Alternatevly, you can install Chrome extension or FF addon

checkio install-plugin
checkio install-plugin --ff
checkio install-plugin --chromium

Read more here about other functionality that the checkio client provides. Feel free to submit an issue in case of any difficulties.

Pair Programming (Beta-version)

Welcome to Pair Programming! Engage in real-time collaboration on coding projects by starting a session and sharing the provided unique URL with friends or colleagues. This feature is perfect for joint project development, debugging, or learning new skills together. Simply click 'Start Session' to begin your collaborative coding journey!

Waiting for Pair Programming to start...

You are trying to join a pair programming session that has not started yet.

Please wait for the session creator to join.

Waiting for Pair Programming to reconnect...

It looks like the creator of the pair programming session closed the editor window.

It might happen accidentally, so that you can wait for reconnection.

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